In assembling a fixed scroll and an orbiting scroll of a conventional scroll compressor, a buildup of dimensional errors and shape errors, for example, of related components responsible for positioning of the two scrolls causes a margin within which the phase shift angle between the two scrolls twists clockwise and counterclockwise from a reference value of 180° during operation. That is, an orbiting scroll of a scroll compressor is known to be twisted in position from the upright position thereof about the center of an end plate during operation, depending on factors such as the specifications and dimensional tolerance of a rotation-preventing mechanism. In the description below, the twist from the upright position is referred to as an “amount of twist in position α”, and the twisting margin depending on, for example, the specifications and dimensional tolerance of a rotation-preventing mechanism is referred to as an “allowable angle of rotation (φ)”.
It is difficult to readily reduce the allowable angle of rotation φ because it depends on, for example, the rotation-preventing function and the machining accuracy. The upright position of an orbiting scroll is the position where an involute surface of a spiral wrap of the orbiting scroll has a phase shift of 180° from an involute surface of a spiral wrap of a fixed scroll.
Disclosed in the conventional art relating to the allowable angle of rotation φ described above as a measure against noise due to the allowable angle of rotation φ and the amount of twist in position α, resulting from gas pressure, is a scroll compressor in which an inner involute surface of a fixed spiral wrap of a fixed scroll is cut to a predetermined depth Δtr to reduce its tooth thickness to Tr−Δtr so that the assembly reference positions of the fixed scroll and the orbiting scroll are substantially twisted from their normal assembly reference positions (positions where the two scrolls have a phase shift of 180°) in a direction opposite an orbiting direction by an appropriate angle (for example, see Patent Document 1).
For a scroll compressor including stepped scrolls to avoid compression leakage during operation, thereby ensuring high compression efficiency, it has been proposed to bring a step of either a spiral or a spiral groove of the orbiting scroll or the fixed scroll farther away from a corresponding step in a rotation direction of the orbiting scroll while bringing the other step closer to a corresponding step in the direction opposite the rotation direction, thus forming asymmetrical shapes (for example, see Patent Document 2).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. HEI-8-49672
Patent Document 2: Japanese Unexamined Patent Application, Publication No. HEI-5-71477